Totoki Koretsugu served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was a retainer of the Bekki clan.

Koretsugu was born as the son of Totoki Koremichi (Magoemon), a bushō in Bungo Province.  Koremichi was the fourth son of Totoki (initially Irikura) Nagato-no-kami, the first head of a branch of the Totoki clan.

Although the timing is unknown, Koretsugu was engaged to serve Bekki Akitsura (Tachibana Dōsetsu), a senior retainer of the Ōtomo, a sengoku daimyō family of Bungo Province.

In 1542, after Mori Shigezane, the lord of Takatoriyama Castle in Chikuzen, defected to the Ōuchi clan, Ōtomo Yoshishige (Sōrin) dispatched an army of 13,000 soldiers to lay siege to the castle.  At this time, Koretsugu led an archery battalion of 500 men in the Tachibana army and climbed halfway up Mount Fukuchi.  By raining down arrows from this location, the forces were able to topple the castle.  For this achievement, Koretsugu received a written commendation.  Later, around the time when Bekki Akitsura adopted the name of Tachibana Dōsetsu, Koretsugu received approximately 74 hectares of land in the village of Itazuke in the Naka District of Chikuzen.

In the fifth month of 1569, at the Battle of Nagao in Chikuzen, Koretsugu and his older brother, Korenori, were killed in action.  The headship of the clan and landholdings were inherited by his second son, Totoki Tsuresada.